编辑代码

#include <bits/stdc++.h>
using namespace std;

int Partition(vector<int>& arr, int left, int right) {
    int pivot = arr[right];
    int i = left - 1;
    for (int j = left; j < right; j++) {
        if (arr[j] >= pivot) {
            i++;
            swap(arr[i], arr[j]);
        }
    }
    swap(arr[i + 1], arr[right]);
    return i + 1;
}

int quickSelect(vector<int>& arr, int left, int right, int k) {
    if (left == right) {
        return arr[left];
    }

    int pivotIndex = Partition(arr, left, right);
    if (k == pivotIndex) {
        return arr[k];
    } else if (k < pivotIndex) {
        return quickSelect(arr, left, pivotIndex - 1, k);
    } else {
        return quickSelect(arr, pivotIndex + 1, right, k);
    }
}

int main() {
    vector<int> arr = {12, 4, 5, 6, 7, 3, 1, 15};
    int n = arr.size();
    int k = 2;
    int result = quickSelect(arr, 0, n - 1, n - k);

    cout << "The " << k << "nd largest element is: " << result;

    return 0;
}